When proteins useful as pharmaceuticals are produced with the recombinant DNA technique, use of animal cells enables complicated post-translational modification and folding which prokaryotic cells can not perform. Therefore, animal cells are frequently used as host cells for producing recombinant proteins.
Recently, a large number of biopharmaceuticals, such as antibodies and physiologically active proteins, have been developed. Techniques that permit efficient production of recombinant proteins by animal cells lead to cost reduction of biopharmaceuticals and promise their stable supply to patients.
Under these circumstances, a method of protein production with higher production efficiency is desired.
Taurine is a type of amino acid present in high concentrations in fish, shell fish and mollusks and is an important nutrient for the growth of mammals. Although taurine is not used in protein synthesis, it has many functions such as normalization of hypercholesterolemia, lowering of blood pressure, detoxication effect, maintenance of immune function, stabilization of biological membranes, regulation of neural excitability, antioxidation, etc. It is known that taurine contributes to osmoregulation and stabilization of cell membrane in cultured cells (Non-Patent Document 1). However, addition of taurine to the medium of astrocyte primary culture where taurine transporter was functioning did not increase taurine uptake into cells (Non-Patent Document 2). Thus, addition of taurine to the medium alone was insufficient.
On the other hand, it is totally unknown whether or not uptake of taurine and other amino acids into cultured cells via taurine transporter contributes to improvement of the production of a desired recombinant protein in the cultured cells.
Several taurine transporters (human: Non-Patent Document 3; mouse: Non-Patent Document 4; and rat: Non-Patent Document 5) and their involvement in the uptake of taurine and other amino acids (e.g., β-alanine) into cells are known (Non-Patent Document 6). However, with respect to hamster taurine transporter, even its existence has not been known yet.
[Non-Patent Document 1]
    Ian Henry Lambert, Neurochemical Research (2004) 29(1), 27-63[Non-Patent Document 2]    Journal of Neurochemistry (2000), 75(3), 919-924[Non-Patent Document 3]    Uchida, S. et al., Proc. Natl. Acad. Sci. U.S.A. (1992) 89 (17), 8230-8234[Non-Patent Document 4]    Liu, Q. R. et al., Proc. Natl. Acad. Sci. U.S.A. (1992) 89 (24), 12145-12149[Non-Patent Document 5]    Smith, K. E. et al., Mol. Pharmacol. (1992) 42 (4), 563-569[Non-Patent Document 6]    Ryo Shioda et al., Investigative Opthalmology & Visual Science (2002) 43 (9), 2916